The goal of this program grant project is to explore the impact of co- occurring disease conditions (i.e. co-morbidity) on the non-fatal health outcomes (i.e. disability) assessed in the Global Burden of Disease Study. This work will provide empirical data on the relationship between morbidity and disability which can be used to improve the methodology of calculating burden in cases where multiple diseases are present. The specific aims of this work: 1) to describe the extent of comorbidity, 2) to examine the effect of co-morbidity on disability, and 3) to examine the changing relationship between comorbidity and disability across the life course in aging populations. Research Design and Methods: Primary and secondary analyses will be used to address each of the specific aims. Because there is little data which specifically addresses the impact of comorbidity on disability, primary data collection will be focused on this issue. Patters of comorbidity will first be identified using a range of statistical techniques including cluster-, factor- and grade of membership-analyses in secondary analyses of large data sets. Once patterns of comorbidity have been identified, the most important groups will be chosen based on prevalence, disability rating and health expenditure, among other criteria. Specific data will be collected internationally on common co-morbid conditions as an additional supplement to an ongoing WHO initiative on World Mental Health Survey 2000 including data on chronic conditions, non-fatal health outcomes and health state preference in general populations samples. Various repression techniques will then be used to examine the impact of co-morbidity on disability. Longitudinal data in the form of serial cross- sectional and panel designs will be used together with regression analyses to address the final aim.